1. Field of the Invention
The present invention is related to light extraction from light emitting diodes (LEDs).
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification. In addition, a list of a number of different publications can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
In a conventional LED, in order to increase the light output power from the front side of the LED, the emitted light is reflected by a mirror placed on the backside of the substrate or is reflected by a mirror coating on the lead frame, even if there are no mirrors on the backside of the sapphire substrate, and even if the bonding material is transparent at the emission wavelength. However, this reflected light is re-absorbed by the emitting layer (active layer), because the photon energy is almost same as the band-gap energy of the light emitting species, such as AlInGaN multi-quantum wells (MQWs). The efficiency or output power of the LEDs is decreased due to this re-absorption of the LED light by the emitting layer. See, for example, FIGS. 1, 2 and 3, which are described in more detail below. See also J. J. Appl. Phys. 34, L797-99 (1995) and J. J. Appl. Phys. 43, L180-82 (2004).
What is needed in the art are LED structures that more effectively extract light. The present invention satisfies that need.